Trigger nginx to restart after config added

Related to #54 and #56.

Gitlab does not start up on the first provision because nginx does not actually watch /etc/nginx/conf.d/. By default it watches /tmp/nginx.d/.

I thought about putting the file in /tmp/nginx.d/, but that location is configurable, so this commit instead just notifies the service directly.
Merge pull request #59 from achaphiv/patch-2

Trigger nginx to restart after config added